C#

//read CSV format files into a dataset
public static DataSet ReadFileAsDataSet(string filePath, string fileName)
{
  OleDbConnection oCon = new OleDbConnection(
    "Provider=Microsoft.Jet.OLEDB.4.0;" +
	"Data Source=" + filePath + ";" +
	"Extended Properties=\"text;HDR=NO;FMT=Delimited\"");

	OleDbDataAdapter oCmd = new OleDbDataAdapter(
	  "select * from "+fileName, oCon);

  DataSet ds = new DataSet();
  oCmd.Fill(ds);
  oCon.Close();
			
  return ds;
}

//write a dataset as a file (currently only supports one table)
//produces files with the following format - "val","val","val","val"
public static void WriteDataSetAsFile(string filepath, string fileName, DataSet ds)
{
  if(File.Exists(filepath + "\\" + fileName))
    File.Delete(filepath + "\\" + fileName);

  StreamWriter sw = new StreamWriter(filepath + "\\" + fileName, true);

  foreach (DataRow dr in ds.Tables[0].Rows)
  {
    object[] objRowData = dr.ItemArray;
    string strRowData = string.Empty;
    foreach(object obj in objRowData)
    {
      strRowData+= "\"" + obj.ToString() + "\",";
    }
    strRowData = strRowData.Remove(strRowData.Length - 1, 1);
    sw.WriteLine(strRowData);
  }
  sw.Close();
}

// Create a new row
DataRow row = dataTable.NewRow();

// Set the row's members
row["Column1"] = "blah";
row["Column2"] = "blech";

// Add the row to the rows collection
dataTable.Rows.Add( row );
// Update the dataset
dataAdapter.Update( dataSet, "TableName" );
// Accept changes
dataSet.AcceptChanges();